The present invention relates to a device and method for transforming a digital signal, such as, a digital filtering device and method. More particularly, this invention is concerned with block-based discrete wavelet transformation according to which an image to be coded is divided into a plurality of blocks that are mutually independently subjected to discrete wavelet transformation (filtering).
Numerous digital filtering methods and devices are known. Discrete cosine transform (DCT) and wavelet transformation are well-known.
These filtering devices and methods are, generally, incorporated as one part or facility of a unit for coding or decoding image data so as to compress or decompress the image data. Moreover, lots of memory spaces or buffer spaces that are randomly accessible are often necessary to store data during processing. For example, in a conventional configuration for performing image processing using wavelet transformation, image data to be placed in a predetermined memory is read first, and then a filtering step is carried out. The memory space is so large as to make it difficult to perform filtering within such an apparatus as a camera, a facsimile system, a printer, or a copier.